Paint can be defined as a liquid, liquefiable, or mastic composition which after application to a substrate as a thin layer is converted to an opaque solid film. A wide variety of paints exist for the automotive industry, the housing industry, the advertising industry, the art industry, etc., with the three most common types of paint classified as lacquers, enamels, and water base. Lacquers typically dry quickly because of solvent evaporation whereas enamels dry through a chemical change or reaction of the material. Within enamel paints, two-stage paints can consist of two distinct layers made from a base coat and a clear coat. The base coat/clear coat enamel paints are typically used to repaint cars and trucks with the base coat being a layer of color applied over a primer-sealer and the clear coat sprayed over the base coat. Water base paints, as implied, use water as the carrier of the paint pigment and dry through evaporation of the water.
The main constituents of paint are pigments, binders or vehicles, solvents, and additional additives. Pigments provide the color to the paint whereas the binder is the actual film-forming component. Solvents are typically used to adjust the curing and/or drying properties and viscosity of the paint which can allow the paint to be sprayed onto a desired substrate. Finally, additives that modify surface tension, improve flow properties, improve surface finish, and the like can be included.
A pigment appears as a particular color because it selectively reflects and absorbs certain wavelengths of light. When white light, i.e. light having a roughly equal mixture of the entire visible spectrum of wavelengths, encounters a pigment, some wavelengths are absorbed by the chemical bonds and substituence of the pigment and other wavelengths are reflected. The reflected wavelengths determine the color of the pigment. This type of coloring mechanism is based on light absorption and the molecular structure generally reflects a broad range of wavelength with a moderate reflectivity (50-60%). In contrast, nature provides magnificent colors and metal-type reflectors in insects, butterflies, birds and fish. Such colors found in nature are not based on pigments, but on the interference of light reflected from either a nanoscopic multilayer structure of alternative high and low refractive index materials or a regular array of nano-sized particles. These types of nanostructure assemblies can reflect up to 100% of the incident light. Such types of nanostructure assemblies, for example multilayer structures, have not been exploited for providing narrow reflection bands of electromagnetic radiation and in particular for providing omnidirectional structural color pigments for paint. Therefore, there is a need for a paint that provides a narrow reflection band, the reflection band being constant when the paint is viewed from various viewing angles.